Manufacturing method of multilayer printed wiring board and multilayer printed wiring board

ABSTRACT

A wiring substrate is manufactured by attaching an adhesive protective film to a metal-foiled laminate sheet, forming bottomed via holes by partially removing the film and an insulating film, filling conductive pastes into the holes, and peeling the film. A wiring substrate is manufactured by forming an adhesive protective layer so as to cover a patterned metal foil on a metal-foiled laminate sheet, forming bottomed step via holes by partially removing the layer and an insulating film, filling conductive pastes into the holes, and peeling off a protective film. The wiring substrate and the second wiring substrate are laminated in such a way that protruding parts of the pastes come into contact with respective protruding parts of the pastes.

TECHNICAL FIELD

The present invention relates to a manufacturing method of a multilayerprinted wiring board and the multilayer printed wiring board. Morespecifically, the present invention relates to a manufacturing method ofa multilayer printed wiring board having three or more wiring layersthat are interlayer-connected through conductive vias formed ofconductive paste and the multilayer printed wiring board.

BACKGROUND ART

Since electronic apparatuses have been downsized and the functionalitiesthereof have been advanced, the high densities of printed wiring boardshaving the various electronic devices mounted thereon have beendemanded. In response to these demands, multi-layered printed wiringboards (multilayer printed wiring boards) have been developed.

To achieve the high density, for example, a hybrid multilayer circuitboard has been developed (Patent Literature 1). The hybrid multilayercircuit board includes two multilayer circuit boards (hard circuitboards) and a flexible printed wiring board (or a flexible flat cable)that connects the multilayer circuit boards.

The above multilayer printed wiring boards and the hybrid multilayercircuit board have been widely used for small electronic devices such aslaptop computers, digital cameras, portable communication devices, andgame machines.

In such electronic devices, the signal transmission speed tends tobecome higher and higher because the amount of information handled bythe electric devices particularly increases. For example, in personalcomputers, the transmission standard shifted to a standard with thetransmission rate of 6 Gbps during 2010 to 2011. The importance ofconsidering the signal loss in transmission lines is increasing.

Conventionally, a transmission line in a printed wiring board thattransfers signals at a high speed is matched with a characteristicimpedance. Accordingly, unnecessary reflection at respective boundariesamong a signal driver, the transmission line, and a signal receiver isprevented, thereby preventing the deterioration in signal quality andsecuring the transmission characteristics. For example, a single endtransmission line is designed generally so as to have a characteristicimpedance of 50Ω.

When the resistive component in a transmission line is neglected, acharacteristic impedance is expressed by Formula 1.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{Z_{0} = \sqrt{\frac{L}{C}}} & (1)\end{matrix}$

In the above formula, Z₀ is a characteristic impedance, L is aninductance, and C is a capacitance.

As is seen from Formula 1, the value of the characteristic impedance isdefined not only by physical properties such as the dielectric constantof the insulating layer, the conductivity of the wiring conductor, thepermeability or the like in the printed wiring board but also byphysical shapes such as the width and thickness of the transmission line(a signal line), the distance (that is, the thickness of the insulatinglayer) between the signal line and the ground layer, and the like.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent No, 2631287-   Patent Literature 2: Japanese Patent Laid-Open No. 2011-66293-   Patent Literature 3: Japanese Patent Laid-Open No. 2007-96121

SUMMARY OF INVENTION Technical Problem

In recent years, due to the increasing signal speeds and the extendedtransmission lines, it is difficult to allow a conventional transmissionloss. Therefore, a method of increasing the thickness of an insulatorlayer (a dielectric layer) forming a transmission line and increasingthe width of a signal line has been applied to reduce the transmissionloss while keeping a characteristic impedance constant. However, thetransmission loss is becoming difficult to allow even by this method.

Accordingly, a liquid crystal polymer (LCP) is beginning to be used foran insulating layer of a flexible printed wiring board. The dielectricloss of the liquid crystal polymer is low due to its low dielectricconstant and low dielectric loss tangent (tan δ) and thereby can reducethe transmission loss.

The dielectric loss has the relation with the dielectric constant anddielectric loss tangent shown in Formula (2).

[Expression 2]

Loss ∝√{square root over (∈)}·tan δ  (2)

In the above formula, Loss is the dielectric loss, ∈ is the dielectricconstant, and tan δ is the dielectric loss tangent.

Of materials that can be practically used for an insulating layer, aliquid crystal polymer is one of materials that have the lowestdielectric constant and dielectric loss tangent. Therefore, when atransmission loss smaller than a transmission loss obtained by thecharacteristics of a liquid crystal polymer is desired, a transmissionloss needs to be reduced by increasing the width of the signal line andthe thickness of the insulating layer as in the above case.

However, the thermal expansion coefficient of a liquid crystal polymerin a thickness direction is larger than that of an insulating material(e.g., polyimide) used in a conventional flexible printed wiring board.For this reason, the thermal expansion coefficient is largely differentfrom that of a plated throughhole that has been generally used as aninter-layer connection path. When the insulating layer of the liquidcrystal polymer is made thick, the reliability in temperature cycle orthe like may be insufficient.

It has been proposed that in a printed wiring board using a liquidcrystal polymer as an insulating layer, conductive vias using conductivepastes are used for an inter-layer connection path instead of platedthroughholes (Patent Literatures 2 and 3). The conductive pastes areobtained by combining metal particles such as copper particles or silverparticles to a resin binder such as epoxy.

However, in Patent Literatures 2 and 3, a multilayer printed wiringboard is manufactured by laminating wiring substrates as many as wiringlayers. Accordingly, the number of processes (piercing by laserprocessing, desmear treatment, printing of conductive pastes, and thelike) for preparing the wiring substrates is large and increase in thenumber of the processes complicates preparation of necessary materials.As a result, the manufacturing cost of the multilayer printed wiringboard increases.

When the number of wiring substrates to be laminated is large, thepositional deviation amount that is a total of the expansion variationof the wiring substrates and the lamination variation during laminatingthe wiring substrates cumulatively increases, thereby deteriorating theyield. On the other hand, when the margin for positional deviation ismade large, the high density of the multilayer printed wiring board isdifficult to achieve.

The present invention has been made based on the above technicalacknowledgements, and an object of the present invention is to provide amultilayer printed wiring board with an excellent yield that can reducethe manufacturing cost and easily achieve the high density.

Solution to Problem

A manufacturing method of a multilayer printed wiring board according toan embodiment of the present invention includes

-   -   attaching an adhesive protective film having a weak adhesive        layer formed on one side thereof to a single-sided metal-foiled        laminate sheet having a first insulating resin film and a first        metal foil on a front face of the first insulating resin film in        such a way that the weak adhesive layer contacts with a rear        face of the first insulating resin film,    -   forming a bottomed via hole that has a bottom face with the        first metal foil exposed therefrom by partially removing the        adhesive protective film and the first insulating resin film,    -   first printing of filling a conductive paste into the bottomed        via hole by a printing method, peeling off the adhesive        protective film from the first insulating resin film and causing        a part of the conductive paste filled in the bottomed via hole        to protrude from the first insulating resin film, and thereby        obtaining a first wiring substrate,    -   forming, on a double-sided metal-foiled laminate sheet having a        second insulating resin film and second and third metal foils        respectively provided on a front face and a rear face of the        second insulating resin film, a piercing mask by patterning the        second metal foil,    -   forming an adhesive protective layer including an adhesive-agent        layer that covers the front face of the second insulating resin        film and buries the patterned second metal foil and a protective        film that is laminated on the adhesive-agent layer,    -   forming a bottomed step via hole that has a middle part with the        piercing mask exposed therefrom and a bottom face with the third        metal foil exposed therefrom by partially removing the adhesive        protective layer and the second insulating resin film,    -   second printing of filling a conductive paste into the bottomed        step via hole by a printing method,    -   peeling off the protective film from the adhesive-agent layer        and causing a part of the conductive paste filled in the        bottomed step via hole to protrude from the adhesive-agent        layer, thereby obtaining a second wiring substrate, and    -   laminating in which the first wiring substrate and the second        wiring substrate are laminated in such a way that a protruding        part of the conductive paste filled in the bottomed via hole of        the first wiring substrate comes into contact with a protruding        part of the conductive paste filled in the bottomed step via        hole of the second wiring substrate, and the laminated first and        second wiring substrates are heated to be integrated with each        other.

Advantage Effects of Invention

In the present invention, the first wiring substrate that is obtained byusing the single-sided metal-foiled laminate sheet as a startingmaterial and causing the part of the conductive paste filled in thebottomed via hole to protrude from the first insulating resin film andthe second wiring substrate that is obtained by using the double-sidedmetal-foiled laminate sheet as a starting material and causing the partof the conductive paste filled in the bottomed step via hole to protrudefrom the adhesive-agent layer are laminated in such a way that theprotruding part of the conductive paste filled in the bottomed via holeof the first wiring substrate comes into contact with the protrudingpart of the conductive paste filled in the bottomed step via hole of thesecond wiring substrate.

The two wiring substrates are laminated in the above manner so that amultilayer printed wiring board having three wiring layers connectedelectrically with one another through conductive vias is provided.

Since the two wiring substrates are sufficient for the three wiringlayers as described above, the number of materials required formanufacturing the multilayer printed wiring board can be reduced and themanufacturing processes can be simplified. Therefore, the manufacturingcost can be reduced and the multilayer printed wiring board can beprovided inexpensively.

Furthermore, since it suffices that only the two wiring substrates arelaminated, deterioration in yield caused by positional deviation can beavoided and the margin for positional deviation does not need to belarge. Therefore, the present invention is effective for achieving thehigh density of the multilayer printed wiring board.

Therefore, the present invention can provide a multilayer printed wiringboard with an excellent yield that can reduce the manufacturing cost andeasily achieve the high density.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a process sectional view for explaining a manufacturingmethod of a wiring substrate 10 of a multilayer printed wiring board 30according to a first embodiment of the present invention.

FIG. 1B is a process sectional view following FIG. 1A for explaining amanufacturing method of the wiring substrate 10 of the multilayerprinted wiring board 30 according to the first embodiment of the presentinvention.

FIG. 2A is a process sectional view for explaining a manufacturingmethod of a wiring substrate 20 of the multilayer printed wiring board30 according to the first embodiment of the present invention.

FIG. 2B is a process sectional view following FIG. 2A for explaining amanufacturing method of the wiring substrate 20 of the multilayerprinted wiring board 30 according to the first embodiment of the presentinvention.

FIG. 3A is a process sectional view for explaining a manufacturingmethod of the multilayer printed wiring board 30 according to the firstembodiment by laminating the wiring substrates 10 and 20.

FIG. 3B is a sectional view of the multilayer printed wiring board 30according to the first embodiment of the present invention.

FIG. 4 is a process sectional view for explaining a manufacturing methodof a wiring substrate 40 of a multilayer printed wiring board 50according to a second embodiment of the present invention,

FIG. 5A is a process sectional view for explaining a manufacturingmethod of the multilayer printed wiring board 50 according to the secondembodiment by laminating the wiring substrates 10, 20, and 40.

FIG. 5B is a sectional view of the multilayer printed wiring board 50according to the second embodiment of the present invention,

FIG. 6 is a process sectional view for explaining a manufacturing methodof a wiring substrate 10A of a multilayer printed wiring board 60according to a third embodiment of the present invention.

FIG. 7 is a process sectional view for explaining a manufacturing methodof a wiring substrate 20A of the multilayer printed wiring board 60according to the third embodiment of the present invention.

FIG. 8 is a process sectional view for explaining a manufacturing methodof a wiring substrate 40A of the multilayer printed wiring board 60according to the third embodiment of the present invention.

FIG. 9A is a process sectional view for explaining a manufacturingmethod of the multilayer printed wiring board 60 according to the thirdembodiment by laminating the wiring substrates 10A, 20A, and 40A.

FIG. 9B is a sectional view of the multilayer printed wiring board 60according to the third embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be explained withreference to the drawings. Components having identical functions aredenoted by same reference characters throughout the drawings anddetailed explanations of a component denoted by a same referencecharacter are not repeated basically. The drawings are schematic and therelation between thicknesses and plane dimensions, the ratio ofthicknesses of layers, and the like in the drawings are different fromthose in the actual state.

First Embodiment

A first embodiment of the present invention will be explained withreference to FIGS. 1A to 3B.

As is clear from FIGS. 3A and 3B, a multilayer printed wiring board 30according to the present embodiment is configured by laminating twowiring substrates (a wiring substrate 10 and a wiring substrate 20).

Explanations of a manufacturing method of the wiring substrate 10 withreference to FIGS. 1A and 1B are followed by explanations of amanufacturing method of the wiring substrate 20 with reference to FIGS.2A and 2B. Explanations of a manufacturing method of the multilayerprinted wiring board 30 with reference to FIGS. 3A and 3B follow theseexplanations.

First, a single-sided metal-foiled laminate sheet 3 having an insulatingresin film 1 and a metal foil 2 on a front face 1 a of the insulatingresin film 1 is prepared as illustrated in (1) of FIG. 1A. Theinsulating resin film 1 is an insulating film (having a thickness of 100μm, for example) formed of a liquid crystal polymer (LOP) or the like.The metal foil 2 is a copper foil (having a thickness of 12 μm, forexample), for example. The metal foil 2 may be formed of metal (e.g.,silver or aluminum) other than copper.

Subsequently, reception lands 2 a and wirings 2 b are formed bypatterning the metal foil 2 by a known photofabrication method. Thediameter of the reception 1 and 2 a is approximately φ250 μm, forexample.

Subsequently, an adhesive protective film 4 is prepared. The adhesiveprotective film 4 is obtained by forming a weak adhesive film (having athickness of 10 μm, for example) on one side of an insulating film(having a thickness of 20 μm, for example) made of PET or the like.

Subsequently, the adhesive protective film 4 having a weak adhesivelayer (not illustrated) formed on one side thereof is attached to thesingle-sided metal-foiled laminate sheet 3 in such a way that the weakadhesive layer contacts with a rear face 1 b of the insulating resinfilm 1 as illustrated in (3) of FIG. 1A.

Subsequently, the adhesive protective film 4 and the insulating resinfilm 1 are partially removed, thereby forming bottomed via holes(bottomed conducting holes) 5 each having a bottom face with the metalfoil 2 exposed therefrom as illustrated in (4) of FIG. 1a The diameterof the bottomed via hole 5 is φ150 to 200 μm, for example.

For example, the bottomed via holes 5 are formed by laser processing. Inview of easiness in processing, an infrared laser such as a carbondioxide laser is preferably used at this step. When a carbon dioxidelaser is used, a beam diameter is made substantially equal to thedesired hole diameter of the bottomed via hole 5. The bottomed via holes5 may be formed using other lasers such as a UV-YAG laser.

Here, the dioxide-gas laser processing machine (ML605GTXIII-5100U2)manufactured by Mitsubishi Electric Corporation is used. The beamdiameter is adjusted to 150 μm with a predetermined aperture or thelike, the plus width is set to 10 μSec, energy per pulse is set to 5 mJ,and thereby forming one bottomed via hole 5 by five shots.

After irradiation of laser pulses, desmear treatment is performed toremove resin residues at the boundary between the insulating resin film1 and the metal foil 2 (the reception lands 2 a) and a treatment film onthe rear face of the metal foil 2. The treatment film on the rear faceof the metal foil 2 is a film (for example, a Ni/Cr film) that has beenformed in manufacturing the single-sided metal-foiled laminate sheet 3in order to improve the adhesion between the metal foil 2 that is acopper foil or the like and the insulating resin film 1.

Subsequently, conductive pastes 6 are filled into the bottomed via holes5 by a printing method (a first printing process) as illustrated in (5)of FIG. 1B. More specifically, while the adhesive protective film 4 isused as a printing mask, the conductive pastes 6 are filled into thebottomed via holes 5 by a printing method such as screen printing. Theconductive pastes 6 are obtained by dispersing metal particles on resinbinder that is a pasty thermosetting resin.

Subsequently, the adhesive protective film 4 is peeled off from theinsulating resin film 1. Accordingly, respective parts (protruding parts6 a) of the conductive pastes 6 filled in the bottomed via holes 5 arecaused to protrude from the insulating resin film 1 as illustrated in(6) of FIG. 1B. The height of the protruding part 6 a is substantiallyequal to the thickness of the adhesive protective film 4.

The above processes provide the wiring substrate 10 illustrated in (6)of FIG. 1B.

Next, a manufacturing method of the wiring substrate 20 will beexplained with reference to FIGS. 2A and 2B.

First, a double-sided metal-foiled laminate sheet 14 having aninsulating resin film 11 and metal foils 12 and 13 respectively placedon a front face 11 a and a rear face 11 b of the insulating resin film11 is prepared as illustrated in (1) of FIG. 2A. The insulating resinfilm 11 is an insulating film (having a thickness of 100 μm, forexample) formed of a liquid crystal polymer or the like. For example,the metal foils 12 and 13 are copper foils (each having a thickness of12 μm, for example). The metal foils 12 and 13 may be made of metalother than copper (e.g., silver, aluminum).

Subsequently, in the double-sided metal-foiled laminate sheet 14,piercing masks 12 a, reception lands 12 b and wirings (not illustrated)are formed by patterning the metal foil 12 by a known photofabricationmethod as illustrated in (2) of FIG. 2A. For example, the diameter ofthe piercing mask 12 a is approximately φ350 μm. For example, thediameter of the reception land 12 b is approximately φ250 μm. Similarly,reception lands 13 a and wirings 13 b are formed by patterning the metalfoil 13. For example, the diameter of the reception land 13 a isapproximately φ250 μm.

The positioning accuracy between the piercing mask 12 a and thereception land 13 a is determined by the exposure accuracy. Therefore,the high positioning accuracy (for example, ±10 μm) can be obtainedrelatively easily, comparing with a conventional case in which twoone-sided substrates are laminated.

Subsequently, an adhesive protective layer 17 that covers and protectsthe patterned metal foil 12 is formed on the double-sided metal-foiledlaminate sheet 14 as illustrated in (3) of FIG. 2A. The adhesiveprotective layer 17 includes an adhesive-agent layer 15 and a protectivefilm 16 laminated on the adhesive-agent layer 15. The adhesive-agentlayer 15 covers the front face 11 a of the insulating resin film 11 andburies the patterned metal foil 12.

The adhesive protective layer 17 can be formed by two kinds of methods,for example. In one method, the adhesive-agent layer 15 is first formedon the insulating resin film 11. For example, a low flow bonding sheethaving a thickness of 15 μm is laminated on the insulating resin film11. Thereafter, the protective film 16 is laminated on theadhesive-agent layer 15. For example, the protective film 16 (having athickness of 20 μm, for example) made of PET or the like is attached tothe adhesive-agent layer 15.

In the other method, a film that is obtained by providing theadhesive-agent layer 15 on one side of the protective film 16 isattached to the insulating resin film 11.

In the both methods, when the adhesive-agent layer 15 or the filmobtained by providing the adhesive-agent layer 15 on one side of theprotective film 16 is laminated, the laminating needs to be performed ata lower temperature than the thermosetting temperature of theadhesive-agent layer 15 so as to fill the patterned metal foil 12 whilemaintaining the adhesiveness required for a laminating process whichwill be described later.

Roughing treatment may be performed to the metal foil 12 before theadhesive protective layer 17 is formed. The roughing treatment canimprove the adhesion strength between the metal foil 12 and theadhesive-agent layer 15. Here, the roughing treatment is performed tothe copper foil that is the metal foil 12 using Neo Brown NB© seriesmanufactured by Ebara-Udylite Co., Ltd.

Subsequently, the adhesive protective layer 17 and the insulating resinfilm 11 are partially removed, thereby forming bottomed step via holes18 a each having a middle part with the piercing mask 12 a exposedtherefrom and a bottom face with the metal foil 13 (the reception land13 a) therefrom as illustrated in (4) of FIG. 2B.

In this process, in addition to the bottomed step via holes 18 a,bottomed via holes 18 b and 18 d and bottomed step via holes 18 c areformed as illustrated in (4) of FIG. 2B. The bottomed via hole 18 b is abottomed via hole that penetrates the adhesive protective layer 17 inthe thickness direction and has a bottom face with the reception land 12b exposed therefrom. The bottomed step via hole 18 c is a bottomed stepvia hole having a same structure as the bottomed step via hole 18 a. Thebottomed via hole 18 d is a bottomed via hole that penetrates theadhesive protective layer 17 and the insulating resin film 11 in thethickness direction and has a bottom face with the reception land 13 aexposed therefrom.

Considering the positional deviation at the laminating process whichwill be described later, the diameter of the bottomed step via hole 18 ais preferably larger than that of the bottomed via hole 5, for example,φ250 to 300 μm.

Here, the above dioxide-gas laser processing machine is used and thebeam diameter is adjusted to 250 μm with a predetermined aperture or thelike, the pulse width is set to 10 μSec, energy per pulse is set to 5mJ, thereby forming one bottomed step via hole 18 a by six shots. In thebottomed via hole 18 b, the beam diameter is adjusted to 200 μm, thepulse width is set to 10 μSec, energy per pulse is set to 5 mJ, therebyforming one bottomed via hole 18 b by two shots. In the bottomed viahole 18 d, the beam diameter is adjusted to 250 μm, the pulse width isset to 10 μSec, energy per pulse is set to 5 mJ, thereby forming onebottomed via hole 18 d by six shots.

After irradiation of laser pulses, desmear treatment is performed to thebottomed step via holes 18 a and 18 c and the bottomed via holes 18 band 18 d. Consequently, resin residues at the boundary between theinsulating resin film 11 and the metal foil 13 (the reception lands 13a) and a treatment film on the rear face of the metal foil 13 as well asresin residues at the boundary between the insulating resin film 11 andthe metal foil 12 (the piercing masks 12 a) and a film formed by theroughing treatment on the front face (the top surface) of the metal foil12 are removed.

Subsequently, conductive pastes 19 are filled into the bottomed step viaholes 18 a and 18 c and the bottomed via holes 18 b and 18 d, by aprinting method (a second printing process) as illustrated in (5) ofFIG. 2B. More specifically, while the protective film 16 is used as aprinting mask, the conductive pastes 19 are filled into the bottomedstep via holes 18 a and 18 c and the bottomed via holes 18 b and 18 d bya printing method such as screen printing. The conductive pastes 19 areobtained by dispersing metal particles on resin binder that is a pastythermosetting resin.

Subsequently, the protective film 16 is peeled off from theadhesive-agent layer 15. Accordingly, respective parts (protruding parts19 a) of the conductive pastes 19 filled in the bottomed step via holes18 a and 18 c and the bottomed via holes 18 b and 18 d protrude from theadhesive-agent layer 15 as illustrated in (6) of FIG. 2B. The height ofthe protruding part 19 a is substantially equal to the thickness of theprotective film 16.

The above processes provide the wiring substrate 20 illustrated in (6)of FIG. 2B.

Next, a manufacturing method of the multilayer printed wiring board 30will be explained with reference to FIGS. 3A and 3B.

The wiring substrate 10 and the wiring substrate 20 are positioned to beopposed to each other and the wiring substrate 10 and the wiringsubstrate 20 are laminated in such a way that the protruding parts 6 aof the conductive pastes 6 come into contact with the respectiveprotruding parts 19 a of the conductive pastes 19 as illustrated in FIG.3A. The laminated wiring substrates 10 and 20 (hereinafter, alsoreferred to as “laminate body”) are heated to be integrated with eachother (the laminating process).

More specifically, the laminate body is heated and pressurized with avacuum press apparatus or a vacuum laminator apparatus. For example, thelaminate body is heated to approximately 200° C. and is pressurized atseveral MPa. This temperature is lower than the softening temperature ofa liquid crystal polymer by 50° C. or more.

When a vacuum press apparatus is used, the laminate body is left underthe above heating and pressurizing condition for approximately 30 to 60minutes, for example. Consequently, heat curing of the adhesive-agentlayer 15 and heat curing of the binder resin of the conductive pastes 6and 19 are completed.

When a vacuum laminator apparatus is used, the heating and pressurizingtime is several minutes. The heat-curing reaction is uncompleted whenthe heating and pressurizing are finished. Therefore, the laminate bodyis transferred from the vacuum laminator apparatus to an oven apparatusand post cure treatment is performed to the laminate body. In the postcure treatment, the laminate body is heated to approximately 200° C. forapproximately 60 minutes, for example. Consequently, heat curing of theadhesive-agent layer 15 and heat curing of the binder resin of theconductive pastes 6 and 19 are completed.

Even when either of a vacuum press apparatus and a vacuum laminatorapparatus is used, heating at a predetermined laminating-processtemperature is performed, thereby causing the metallic bonding among themetallic particles included in the conductive pastes 6 and 19 as well asthe metallic bonding among the metallic particles and the metal foils 2,12, and 13 (the reception lands 2 a, 12 b, and 13 a and the piercingmasks 12 a). Consequently, conductive vias 31 to 34 for interlayerconnection are formed as illustrated in FIG. 3B. Furthermore, thisheating substantially completes both of the heat-curing reaction of theresin binder of the conductive pastes 6 and 19 and the heat-curingreaction of the adhesive-agent layer 15.

To achieve the metallic bonding among the metallic particles included inthe conductive pastes 6 and 19 by the heating at the laminating-processtemperature (for example, approximately 200° C.), the melting point ofthe metallic particles is preferably lower than the laminating-processtemperature. Examples of metal having such a low melting point includeIn, SnIn, and SnBi. Therefore, in the above printing processes (thefirst printing process and/or the second printing process) of conductivepastes, the conductive pastes to be used here preferably include metalparticles made of the above metal having a low melting point.

When the metal foils 11, 12, and 13 are copper foils, conductive pastesincluding metal particles made of Sn, Zn, Al, Ag, Ni, Cu or an alloy ofthese metals are preferably used in the above printing processes (thefirst printing process and/or the second printing process) of conductivepastes. Accordingly, the heating at the laminating-process temperature(for example, approximately 200° C.) causes the metallic particlesincluded in the conductive pastes 6 and 19 to form an alloy layer withthe copper foils to achieve the metallic bonding.

After the above laminating process, surface treatment to a wiring layerthat is exposed to the outside, forming of a solder resist or the like,and outer-shape processing are performed as needed.

The above processes provide the wiring layer (the first wiring layer)including the reception lands 2 a and the wirings 2 b, the inside wiringlayer (the second wiring layer) including the piercing masks 12 a andthe reception lands 12 b, and the wiring layer (the third wiring layer)including the reception lands 13 a and the wirings 13 b as illustratedin FIG. 3B.

As illustrated in FIG. 3B, the multilayer printed wiring board 30includes the insulating resin film 11, the reception lands 13 a on thelower face of the insulating resin film 11, the piercing masks 12 a onthe upper face of the insulating resin film 11, the insulating resinfilm 1 laminated on the upper face of the insulating resin film 11through the adhesive-agent layer 15 burring the piercing masks 12 a, thereception lands 2 a on the upper face of the insulating resin film 1,and the conductive vias 31 to 34.

The conductive via 31 is provided to penetrate the insulating resin film11, the adhesive-agent layer 15, and the insulating resin film 1 in thethickness direction and connects the reception lands 13 a, the receptionlands 2 a, and the piercing masks 12 a electrically with one another. Inthis way, the conductive via 31 connects all of the first to thirdwiring layers electrically.

In contrast, the conductive via 32 connects the first wiring layer andthe second wiring layer electrically, the conductive via 33 connects thesecond wiring layer and the third wiring layer electrically, and theconductive via 34 connects the first wiring layer and the third wiringlayer electrically. In this way, all the combinations of interlayerconnection are achieved.

As illustrated in FIG. 3B, more specifically, the conductive via 31includes an upper conductive via part 31 a that penetrates theinsulating resin film 1 in the thickness direction and a lowerconductive via part 31 b that penetrates the adhesive-agent layer 15 andthe insulating resin film 11 in the thickness direction. The upperconductive via part 31 a and the lower conductive via part 31 b comeinto contact with each other at the interface between the insulatingresin film 1 and the adhesive-agent layer 15.

The upper conductive via part 31 a is formed by curing the conductivepaste filled in the bottomed via hole that has a bottom face with thereception land 2 a exposed therefrom. The lower conductive via part 31 bis formed by curing the conductive paste filled in the bottomed step viahole that has a middle part with the piercing mask 12 a exposedtherefrom and a bottom face with the reception land 13 a exposedtherefrom.

The conductive via 32 is formed by causing conductive via parts 32 a and32 b to come into contact with each other at the interface between theinsulating resin film 1 and the adhesive-agent layer 15. The conductivevia 34 is formed by causing conductive via parts 34 a and 34 b to comeinto contact with each other at the interface between the insulatingresin film 1 and the adhesive-agent layer 15.

In the above manufacturing method of the multilayer printed wiring board30, the metal foil 2 and the metal foil 13 are patterned to formrespective predetermined wiring patterns before the laminating processof laminating and integrating the wiring substrate 10 and the wiringsubstrate 20. However, the present invention is not limited to the abovemanufacturing method. That is, the metal foil 2 and the metal foil 13are patterned to form respective predetermined wiring patterns after thelaminating process. In this case, the patterning can be performed whilepositioning to the second wiring layer has been performed. Thus, thefirst and third wiring layers can be formed with higher accuracy.Moreover, this method is effective when the variation in dimensionalcontraction of the wiring substrates 10 and 20 is large in thelaminating process.

The metal foil 2 and the metal foil 13 may be patterned simultaneouslyby both-side simultaneous exposure. In this case, the positioning of thefirst wiring layer and the third wiring layer can be performed withhigher accuracy than the positional accuracy (the laminating accuracy)of laminating the wiring substrate 10 and the wiring substrate 20.

The thicknesses of the adhesive protective film 4 and the protectivefilm 16 define the heights (the protruding amounts of the conductivepastes) of the protruding parts 6 a and 19 a of the conductive pastes 6and 19. When these films are excessively thick, the protruding parts 6 aand 19 a excessively protrude. Thus, the adhesive-agent layer 15 cannotabsorb the unevenness on the multilayer printed wiring board 30completely in the laminating process and flatness of the multilayerprinted wiring board 30 may be deteriorated. On the other hand, whenthese films are excessively thin, the heights of the protruding parts 6a and 19 a are excessively low. Thus, even when the laminate body ispressurized in the laminating process, the bonding between the conducivevia parts (for example, the conductive via part 31 a and the conductivevia part 31 b) is weak so that the connection reliability of theconductive vias 31, 32, and 34 may be insufficient. Therefore, each ofthe thicknesses of the adhesive protective film 4 and the protectivefilm 16 is preferably in a range of 20±10 μm, more preferably in a rangeof 20±5 μm.

In the above first and second printing processes, in order to preventthe contamination of air voids, the printing of the conductive pastes 6and 19 are performed preferably under vacuum environment. For example, avacuum printer for screen printing is preferably used. Thus, even when avoid (an area not filled with a conductive paste) is generated duringthe printing, the void disappears by being pressed by the atmosphere atthe release of the vacuum state. In this way, air voids are preventedfrom generating. However, when the diameters of the bottomed via holes 5or the bottomed step via holes 18 a are relatively small, theprobability of air voids generating is low and the printing under avacuum environment is not always necessary.

As described above, in the first embodiment, the multilayer printedwiring board 30 having three wiring layers that are connectedelectrically with one another via conductive vias is manufactured bylaminating two wiring substrates (the wiring substrate 10 and the wiringsubstrate 20).

Since the two wiring substrates are sufficient for the three wiringlayers as described above, the number of materials required formanufacturing the multilayer printed wiring board can be reduced and themanufacturing process can be simplified. Therefore, the manufacturingcost can be reduced and the multilayer printed wiring board 30 can beprovided inexpensively.

Since it suffices that only two wiring substrates are laminated,deterioration in yield caused by positional deviation can be avoided andthe margin for positional deviation does not need to be large.Therefore, the above manufacturing method is effective for achieving thehigh density of the multilayer printed wiring board.

Therefore, according to the first embodiment, it is possible to providea multilayer printed wiring board with an excellent yield that canreduce the manufacturing cost and easily achieve the high density

Second Embodiment

A second embodiment of the present invention will be explained withreference to FIGS. 4, 5A and 5B. One of the differences between thesecond embodiment and the first embodiment is the number of wiringlayers. While the multilayer printed wiring board 30 according to firstembodiment has three wiring layers, a multilayer printed wiring board 50according to the second embodiment has four wiring layers.

As is clear from FIGS. 5A and 5B, the multilayer printed wiring board 50according to the present embodiment is configured by laminating threewiring substrates (the wiring substrate 10, the wiring substrate 20, anda wiring substrate 40).

The manufacturing methods of the wiring substrate 10 and the wiringsubstrate 20 are identical to those in the first embodiment, andtherefore, detailed explanations thereof are omitted.

A manufacturing method of the wiring substrate 40 will be explained withreference to FIG. 4.

First, a single-sided metal-foiled laminate sheet 23 having aninsulating resin film 21 and a metal foil 22 on a rear face 21 b of theinsulating resin film 21 is prepared as illustrated in (1) of FIG. 4.The insulating resin film 21 (having a thickness of 100 for example) isformed of a liquid crystal polymer (LOP) or the like. The metal foil 22is a copper foil or the like (having a thickness of 12 μm, for example).The metal foil 22 may be formed of metal (e.g., silver or aluminum)other than copper.

Subsequently, in the single-sided metal-foiled laminate sheet 23,reception lands 22 a and wirings 22 b are formed by patterning the metalfoil 22 by a known photofabrication method. The diameter of thereception land 22 a is approximately φ250 μm, for example.

Subsequently, an adhesive protective layer 26 is formed on a front face21 a of the single-sided metal-foiled laminate sheet 23 as illustratedin (2) of FIG. 4. The adhesive protective layer 26 includes anadhesive-agent layer 24 that covers the front face 21 a of theinsulating resin film 21 and a protective film 25 that is laminated onthe adhesive-agent layer 24. The forming method of the adhesiveprotective layer 26 is identical to that of the adhesive protectivelayer 17 in the first embodiment, and therefore, explanations thereofare omitted.

Subsequently, the adhesive protective layer 26 and the insulating resinfilm 21 are partially removed, thereby forming bottomed via holes 27each having a bottom face with the metal foil 22 (a reception land 22 a)exposed therefrom as illustrated in (3) of FIG. 4. The forming method ofthe bottomed via hole 27 is identical to that of the bottomed via hole18 d or the like in the first embodiment, and therefore, explanationsthereof are omitted.

Subsequently, conductive pastes 28 are filled into the bottomed viaholes 27 by a printing method as illustrated in (4) of FIG. 4. Thefilling method of the conductive pastes 28 is identical to that of theconductive pastes 6 or the like in the first embodiment, and therefore,explanations thereof are omitted.

Subsequently, the protective film 25 is peeled off from theadhesive-agent layer 24, thereby causing respective parts (protrudingparts 28 a) of the conductive pastes 28 filled in the bottomed via holes27 to protrude from the adhesive-agent layer 24 as illustrated in (4) ofFIG. 4.

The above processes provide the wiring substrate 40 illustrated in (4)of FIG. 4.

A manufacturing method of the multilayer printed wiring board 50 will beexplained with reference to FIGS. 5A and 5B.

As illustrated in FIG. 5, the wiring substrate 10, the wiring substrate20, and the wiring substrate 40 are positioned to be opposed to oneanother and the wiring substrate 10, the wiring substrate 20, and thewiring substrate 40 are laminated in such a way that the protrudingparts 6 a of the conductive pastes 6 come into contact with therespective protruding parts 19 a of the conductive pastes 19 and theprotruding parts 28 a of the conductive pastes 28 come into contact withthe respective reception lands 13 a of the wiring substrate 20. Thelaminated wiring substrates 10, 20, and 40 are heated to be integratedwith one another (a laminating process). The laminating process isidentical to that in the first embodiment, and therefore, detailedexplanations thereof are omitted.

The above processes provide the multilayer printed wiring board 50having first to fourth wiring layers as illustrated in FIG. 5B. Thefirst to third wiring layers are identical to those in the firstembodiment and the fourth wiring layer is the lowest wiring layerincluding the reception lands 22 a and the wirings 22 b.

As illustrated in FIG. 5B, the multilayer printed wiring board 50includes conductive vias 51 to 53. The conductive vias 51 and 52 connectall of the first to fourth wiring layers electrically. The conductivevia 53 connects the first wiring layer, the third wiring layer, and thefourth wiring layer electrically by skipping the second wiring layer.

The conductive via 51 is formed of conductive via parts 51 a, 51 b, and51 c 1 The conductive via 52 is formed of conductive via parts 52 a, 52b, and 52 c. The conductive via 53 is formed of conductive via parts 53a, 53 b, and 53 c.

As is clear from FIGS. 3B and 5B, a conductive via for connecting anytwo or more layers of the first to fourth wiring layers can be formed.

As described above, in the second embodiment, the multilayer printedwiring board 50 having four wiring layers connected electrically withone another through the conductive vias is manufactured by laminatingthree wiring substrates (the wiring substrate 10, the wiring substrate20, and the wiring substrate 40).

According to the second embodiment, the three wiring substrates aresufficient for the four wiring layers. Thus, the number of materialsrequired for manufacturing the multilayer printed wiring board can bereduced and the manufacturing process can be simplified.

Since it suffices that only three wiring substrates are laminated,deterioration in yield caused by positional deviation can be avoided.Since the margin for positional deviation does not need to be large, theabove manufacturing method is effective for achieving the high densityof the multilayer printed wiring board.

Therefore, according to the second embodiment, it is possible to providea multilayer printed wiring board with an excellent yield that canreduce the manufacturing cost and easily achieve the high density

Third Embodiment

A third embodiment of the present invention will be explained withreference to FIGS. 6 to 9B. Similarly to the second embodiment, thethird embodiment is a multilayer printed wiring board having four wiringlayers. One of the differences between the third embodiment and thesecond embodiment is the positions of piercing masks. That is, while thepiercing masks 12 a are formed only on one main surface of theinsulating resin film 11 in the second embodiment, lands (piercingmasks) having a large diameter are formed on the both sides of theinsulating resin film in order to achieve the high density in the thirdembodiment.

As is clear from FIGS. 9A and 9B, a multilayer printed wiring board 60according to the present embodiment is configured by laminating threewiring substrates (a wiring substrate 10A, a wiring substrate 20A, and awiring substrate 40A).

Explanations of a manufacturing method of the wiring substrate 10A withreference to FIG. 6, explanations of a manufacturing method of thewiring substrate 20A with reference to FIG. 7, and explanations of amanufacturing method of the wiring substrate 40A with reference to FIG.8 will be given in this order. Thereafter, a manufacturing method of themultilayer printed wiring board 60 will be explained with reference toFIGS. 9A and 9B.

A manufacturing method of the wiring substrate 10A will be explainedwith reference to FIG. 6.

First, the single-sided metal-foiled laminate sheet 3 that has beenexplained in the first embodiment is prepared. Thereafter, the receptionlands 2 a and the wirings 2 b are formed by patterning the metal foil 2by a known photofabrication method as illustrated in (1) of FIG. 6.

Subsequently, an adhesive protective layer 9A is formed on the rear face1 b of the single-sided metal-foiled laminate sheet 3 as illustrated in(1) of FIG. 6. The adhesive protective layer 9A includes anadhesive-agent layer 7A that covers the rear face 1 b of the insulatingresin film 1 and a protective film 8A that is laminated on theadhesive-agent layer 7A. The forming method of the adhesive protectivelayer 9A is identical to that of the adhesive protective layer 17 in thefirst embodiment, and therefore, explanations thereof are omitted.

Subsequently, the adhesive protective layer 9A and the insulating resinfilm 1 are partially removed, thereby forming bottomed via holes eachhaving a bottom face with the metal foil 2 (the reception land 2 a)exposed therefrom. Thereafter, a conductive pastes 6A are filled intothe bottomed via holes by a printing method.

Subsequently, the protective film 8A is peeled off from theadhesive-agent layer 7A, thereby causing respective parts of theconductive pastes 6A to protrude from the adhesive-agent layer 7A asillustrated in (3) of FIG. 6.

The above processes provide the wiring substrate 10A illustrated in (3)of FIG. 6.

Next, a manufacturing method of the wiring substrate 20A will beexplained with reference to FIG. 7.

First, the double-sided metal-foiled laminate sheet 14 that has beenexplained in the first embodiment is prepared. Thereafter, the piercingmasks 12 a, the reception lands 12 b and the wirings 12 c are formed bypatterning the metal foil 12 by a known photofabrication method asillustrated in (1) of FIG. 7. Similarly, the reception lands 13 a, thewirings 13 b, and piercing masks 13 c are formed by patterning the metalfoil 13. In this way, in the third embodiment, the piercing masks areformed on the both sides of the double-sided metal-foiled laminate sheet14.

Subsequently, an adhesive protective film 35 having a weak adhesivelayer (not illustrated) formed on one side thereof is attached to thedouble-sided metal-foiled laminate sheet in such a way that the weakadhesive layer contacts with the front face 11 a of the insulating resinfilm 11 and buries the patterned metal foil 12 (the piercing masks 12 a,the reception lands 12 b, and the wirings 12 c) as illustrated in (1) ofFIG. 7.

Also, an adhesive protective film 36 having a weak adhesive layer formedon one side thereof is attached to the double-sided metal-foiledlaminate sheet 14 in such a way that the weak adhesive layer (notillustrated) contacts with the rear face 11 b of the insulating resinfilm 11 and buries the patterned metal foil 13 (the reception lands 13a, the wiring 13 b, and the piercing masks 13 c) as illustrated in (1)of FIG. 7.

Subsequently, the adhesive protective film 35 and the insulating resinfilm 11 are partially removed, thereby forming bottomed step via holeseach having a middle part with the piercing mask 12 a exposed therefromand a bottom face with the reception land 13 a exposed therefrom, andthereafter, conductive pastes 190 are filled into the bottomed via holesby a printing method as illustrated in (2) of FIG. 7.

Also, the adhesive protective film 36 and the insulating resin film 11are partially removed, thereby forming bottomed step via holes eachhaving a middle part with the piercing mask 13 c exposed therefrom and abottom face with the reception land 12 b exposed therefrom, andthereafter, conductive pastes 19D are filled into the bottomed step viaholes using a printing method as illustrated in (2) of FIG. 7.

The conductive pastes 19C and 19D may be printed after the bottomed stepvia holes are formed on the both sides of the double-sided metal-foiledlaminate sheet 14.

Subsequently, the adhesive protective film 35 is peeled off from theinsulating resin film 11, thereby causing respective parts of theconductive pastes 19C to protrude from the piercing masks 12 a asillustrated in (3) of FIG. 7. Similarly, the adhesive protective film 36is peeled off from the insulating resin film 11, thereby causingrespective parts of the conductive pastes 190 to protrude from thepiercing masks 13 c.

The above processes provide the wiring substrate 20A illustrated in (3)of FIG. 7.

Next, a manufacturing method of the wiring substrate 40A will beexplained with reference to FIG. 8.

First, the single-sided metal-foiled laminate sheet 23 that has beenexplained in the second embodiment is prepared. Thereafter, in thesingle-sided metal-foiled laminate sheet 23, the reception lands 22 aand the wirings 22 b are formed by patterning the metal foil 22 by aknown photofabrication method as illustrated in (1) of FIG. 8.

Subsequently, an adhesive protective layer 9B is formed on the frontface 21 a of the single-sided metal-foiled laminate sheet 23 asillustrated in (1) of FIG. 8. The adhesive protective layer 9B includesan adhesive-agent layer 7B that covers the front face 21 a of theinsulating resin film 21 and a protective film 8B that is laminated onthe adhesive-agent layer 7B. The forming method of the adhesiveprotective layer 9B is identical to that of the adhesive protectivelayer 17 in the first embodiment, and therefore, explanations thereofare omitted.

Subsequently, the adhesive protective layer 9B and the insulating resinfilm 21 are partially removed, thereby forming bottomed via holes eachhaving a bottom face with the metal foil 22 (the reception land 22 a)exposed therefrom, and thereafter, conductive pastes 28A are filled intothe bottomed via holes by a printing method, as illustrated in (2) ofFIG. 8.

Subsequently, the protective film 8B is peeled off from theadhesive-agent layer 7B, thereby causing respective parts of theconductive pastes 28A from the adhesive-agent layer 7B as illustrated in(3) of FIG. 8.

The above processes provide the wiring substrate 40A illustrated in (3)of FIG. 8.

Next, a manufacturing method of the multilayer printed wiring board 60will be explained with reference to FIGS. 9A and 9B.

As illustrated in FIG. 9A, the wiring substrate 10A, the wiringsubstrate 20A, and the wiring substrate 40A are laminated in such a waythat the protruding parts of the conductive pastes 6A of the wiringsubstrate 10A come into contact with the respective protruding parts ofthe conductive pastes 190 of the wiring substrate 20A and the protrudingparts of the conductive pastes 28A of the wiring substrate 40A come intocontact with the respective reception lands 13 a of the wiring substrate20A. The wiring substrates 10A, 20A, and 40A that are laminated in thisway are heated to be integrated with one another (a laminating process).The laminating process is identical to that in the first embodiment, andtherefore, detailed explanations thereof are omitted.

The above processes provide the multilayer printed wiring board 60having the first to fourth wiring layers as illustrated in FIG. 9B. Thefirst to fourth wiring layers are identical to those that have beenexplained in the second embodiment.

As illustrated in FIG. 9B, the multilayer printed wiring board 60includes conductive vias 61 to 63. The conductive vias 61 and 62 connectall of the first to fourth wiring layers electrically. The conductivevia 63 connects the first wiring layer, the third wiring layer, and thefourth wiring layer electrically by skipping the second wiring layer.

The conductive via 61 is formed of conductive via parts 61 a, 61 b, and61 c. The conductive via 62 is formed of conductive via parts 62 a, 62b, and 62 c. The conductive via 63 is formed of conductive via parts 63a, 63 b, and 63 c.

As is clear from FIGS. 3B and 9B, a conductive via connecting any two ormore layers of the first to fourth wiring layers can be formed.

As described above, in the third embodiment, the multilayer printedwiring board 60 having four wiring layers connected electrically withone another through the conductive vias is manufactured by laminatingthree wiring substrates (the wiring substrate 10A, the wiring substrate20A, and the wiring substrate 40A).

According to the third embodiment, three wiring substrates aresufficient for four wiring layers. Thus, the number of materialsrequired for manufacturing the multilayer printed wiring board can bereduced and the manufacturing process can be simplified.

Since it suffices that only the three wiring substrates are laminated,deterioration in yield caused by positional deviation can be avoided.Since the margin for positional deviation does not need to be large, theabove manufacturing method is effective for achieving the high densityof the multilayer printed wiring board.

Furthermore, in the third embodiment, the piercing masks having a largediameter are formed on the both sides of the insulating resin film,thereby averaging the pattern densities of the front and rear faces ofthe insulating resin film 11. Thus, the high density of the entiremultiple printed wiring board can be achieved.

Therefore, according to the third embodiment, it is possible to providea multilayer printed wiring board with an excellent yield that canreduce the manufacturing cost and easily achieve the high density.

Three embodiments according to the present invention have beenexplained. In these embodiments, the multilayer printed wiring boardhaving three or four wiring layers has been explained. However, thepresent invention can be also applied to a multilayer printed wiringboard having five or more wiring layers.

The above insulating resin films 1, 11, and 21 are not limited to aliquid crystal polymer film. For example, the insulating resin films 1,11, and 21 may be an insulating resin film such as a polyimide film or apolyethylene terephthalate that is used for a flexible printed wiringboard, or may be formed of a hard insulating resin such as glass epoxy.

Those skilled in the art may conceive additional effects and variousmodifications of the present invention based on the above descriptions.However, an aspect of the present invention is not limited to theembodiments that have been explained above. Constituent requirementsfrom the different embodiments may be combined as appropriate. Variousadditions, modifications, and partial removal can be made within theconceptual ideas and principles of the present invention derived fromthe subjects set forth in the claims and the equivalent thereof.

REFERENCE SIGNS LIST

-   1, 11, 21 INSULATING RESIN FILM-   1 a, 11 a. 21 a FRONT FACE-   1 b, 11 b, 21 b REAR FACE-   2, 12, 13, 22 METAL FOIL-   2 a RECEPTION LAND-   2 b WIRING-   3, 23 SINGLE-SIDED METAL-FOILED LAMINATE SHEET-   4, 35, 36 ADHESIVE PROTECTIVE FILM-   5, 18 b, 18 d, 27 BOTTOMED VIA HOLE-   6, 6A, 19, 19A, 19B, 19C, 19D, 28, 28A CONDUCTIVE PASTE-   6 a, 19 a, 28 a PROTRUDING PART-   7A, 7B, 15, 15A, 15B, 247 ADHESIVE-AGENT LAYER-   8A, 8B, 16, 16A, 16B, 25 PROTECTIVE FILM-   9A, 17, 17A, 17B, 26 ADHESIVE PROTECTIVE LAYER-   10, 10A, 20, 20A, 40, 40A WIRING SUBSTRATE-   12 a, 13 c PIERCING MASK-   12 b, 13 a, 22 a RECEPTION LAND-   12 c, 13 b, 22 b WIRING-   14 DOUBLE-SIDED METAL-FOILED LAMINATE SHEET-   18 a, 18 c BOTTOMED STEP VIA HOLE-   30, 50, 60 MULTILAYER PRINTED WIRING BOARD-   31, 32, 33, 34, 51, 52, 53, 61, 62, 63 CONDUCTIVE VIA-   31 a UPPER CONDUCTIVE VIA PART-   31 b LOWER CONDUCTIVE VIA PART-   32 a, 32 b, 34 a, 34 b, 51 a, 51 b, 51 c, 52 a, 52 b, 52 c, 53 a, 53    b, 53 c, 61 a,-   61 b. 61 c, 62 a, 62 b, 62 c, 63 a, 63 b, 63 c CONDUCTIVE VIA PART

1. A manufacturing method of a multilayer printed wiring boardcomprising: forming, in a first single-sided metal-foiled laminate sheethaving a first insulating resin film and a first metal foil on a frontface of the first insulating resin film, a first adhesive protectivelayer having a first adhesive-agent layer that covers a rear face of thefirst insulating resin film and a first protective film that islaminated on the adhesive-agent layer; forming a first bottomed via holehaving a bottom face with the first metal foil exposed therefrom bypartially removing the first adhesive protective film and the firstinsulating resin film; first printing of filling a conductive paste intothe first bottomed via hole by a printing method; peeling off the firstprotective film from the first adhesive-agent layer and causing a partof the conductive paste filled in the first bottomed via hole toprotrude from the first adhesive-agent layer, thereby obtaining a firstwiring substrate; forming, in a double-sided metal-foiled laminate sheethaving a second insulating resin film and second and third metal foilsrespectively provided on a front face and a rear face of the secondinsulating resin film; a first piercing mask and a first reception landby patterning the second metal foil and forming a second piercing maskand a second reception land by patterning the third metal foil;attaching a first adhesive protective film having a weak adhesive layerformed on one side thereof to the double-sided metal-foiled laminatesheet in such a way that the weak adhesive layer contacts with a frontface of the second insulating resin film and buries the patterned secondmetal foil; attaching a second adhesive protective film having a weakadhesive layer formed on one side thereof to the double-sidedmetal-foiled laminate sheet in such a way that the weak adhesive layercontacts with a rear face of the second insulating resin film and buriesthe patterned third metal foil; forming a first bottomed step via holehaving a middle part with the first piercing mask exposed therefrom anda bottom face with the second reception land exposed therefrom bypartially removing the first adhesive protective layer and the secondinsulating resin film; forming a second bottomed step via hole having amiddle part with the second piercing mask exposed therefrom and a bottomface with the first reception land exposed therefrom by partiallyremoving the second adhesive protective layer and the second insulatingresin film; second printing of filling a conductive paste into the firstbottomed step via hole by a printing method; third printing of filling aconductive paste into the second bottomed step via hole by a printingmethod; peeling off the first adhesive protective film from the secondinsulating resin film and causing a part of the conductive paste filledin the first bottomed step via hole to protrude from the first piercingmask, and peeling off the second adhesive protective film from thesecond insulating resin film and causing a part of the conductive pastefilled in the second bottomed step via hole to protrude from the secondpiercing mask, thereby obtaining a second wiring substrate; forming, ina second single-sided metal-foiled laminate sheet having a thirdinsulating resin film and a fourth metal foil on a rear face of thethird insulating resin film, a second adhesive protective layer having asecond adhesive-agent layer that covers a front face of the thirdinsulating resin film and a second protective film that is laminated onthe second adhesive-agent layer; forming a second bottomed via holehaving a bottom face with the fourth metal foil exposed therefrom bypartially removing the second adhesive protective layer and the thirdinsulating resin film; fourth printing of filling a conductive pasteinto the second bottomed via hole by a printing method; peeling off thesecond protective film from the second adhesive-agent layer and causinga part of the conductive paste filled in the second bottomed via hole toprotrude from the second adhesive-agent layer, thereby obtaining a thirdwiring substrate; and laminating in which the first to third wiringsubstrates are laminated in such a way that a protruding part of theconductive paste filled in the first bottomed via hole of the firstwiring substrate comes into contact with a protruding part of theconductive paste filled in the first bottomed step via hole of thesecond wiring substrate and a protruding part of the conductive pastefilled in the second bottomed via hole of the third wiring substratecomes into contact with the second reception land of the second wiringsubstrate, and the laminated first to third wiring substrates are heatedto be integrated with one another.
 2. The manufacturing method of amultilayer printed wiring board according to claim 1, wherein in thelaminating, the first to third wiring substrates are laminated, therebycausing the protruding part of the conductive paste filled in the firstbottomed via hole of the first wiring substrate to come into contactwith the first reception land of the second wiring substrate and causingthe protruding part of the conductive paste filled in the secondbottomed via hole of the third wiring substrate to come into contactwith the protruding part of the conductive paste filled in the secondbottomed step via hole of the second wiring substrate.
 3. Themanufacturing method of a multilayer printed wiring board according toclaim 1, wherein heating is performed at a predeterminedlaminating-process temperature in the laminating, thereby achievingmetal bonding among metal particles included in the conductive pastesfilled in the first and second bottomed via holes and the first andsecond bottomed step via holes and metal bonding among the metalparticles and the first to fourth metal foils, and substantiallycompleting heat-curing reaction of resin binder included in theconductive pastes and the first and second adhesive-agent layers.
 4. Themanufacturing method of a multilayer printed wiring board according toclaim 1, wherein in at least one of the first to fourth printing, aconductive paste that includes metal particles made of In, SnIn, or SnBiis used.
 5. The manufacturing method of a multilayer printed wiringboard according to claim 1, wherein the first to fourth metal foils arecopper foils, and in at least one of the first to fourth printing, aconductive paste that includes metal particles made of Sn, Zn, Al, Ag,Ni, Cu or an alloy of these metals is used.
 6. The manufacturing methodof a multilayer printed wiring board according to claim 1, whereinbefore the laminating, the first metal foil and the fourth metal foilare patterned to form respective predetermined wiring patterns.
 7. Themanufacturing method of a multilayer printed wiring board according toclaim 1, wherein after the laminating, the first metal foil and thefourth metal foil are patterned to form respective predetermined wiringpatterns.
 8. The manufacturing method of a multilayer printed wiringboard according to claim 7, wherein the first metal foil and the fourthmetal foil are simultaneously patterned by both-side simultaneousexposure.